Many modern devices can be controlled with a remote control unit. For example, television sets, video cassette recorders and stereo/audio systems typically come with a remote control unit that can be used to control that device from a distance.
Typically a remote control unit is a unidirectional, point-to-point communications device for transmitting user input to the device being controlled. Many remote control units operate using an infra-red signal to transmit user input to the device being controlled. This generally requires a line-of-sight between the remote control unit and the controlled device. Some remote control units signal the device controlled with a radio frequency (RF) signal. This allows the remote control unit to signal and control the device without being in view of the device.
Each remote control unit has a specific, fixed protocol that is used to communicate with the device being controlled. The protocol is defined and programmed into the remote control unit and the controlled device by the manufacturer. This is done so that multiple remote controls can be used simultaneously to control multiple devices, with the signal from each remote control unit being recognized and used only by the device built to communicate with that remote control unit.
Some remote control units are designed to support multiple communication protocols so as to be able to control multiple devices, even devices from different manufacturers. Such remote control units are programmed with a variety of different communication protocols. The protocol being used by the remote control unit can then be switched using controls on the remote control unit itself. In this way, the user can selectively operate the remote control unit to send commands to a number of different controlled devices.